1. Field of the Invention
This invention is generally related to a method and apparatus for electrophotographic printing in which a charge image is placed directly on a conventional paper product and, more particularly, to a method and apparatus of electrophotographic printing in which the paper product to be printed upon is interposed between a developer and a layer of photoconductive material whereby toner is deposited directly on the conventional paper product.
2. Description of the Related Art
In the field of electrophotography, the process for printing a toned image on a sheet of conventional paper involves a series of eight steps. In the first step, a charge corotron or alternative, compatible charging means establishes a uniform charge on the surface of a photoconductor. Typically, the photoconductor takes the form of an outer surface on a rotating drum or a linearly moving photoconductor belt. Thus, as the drum rotates past the charge corotron, a charge is placed thereon. Thereafter, in the second step of this process, a latent image is borne electronically on the photoconductor through a laser source arranged in a configuration matching the image to be printed. For example, in a xerographic copier, a high intensity light source is reflected off of the document to be copied and onto the surface of the photoconductor. Thus, in the area of the document where no printing appears, the light source is strongly reflected onto the surface of the photoconductor. Conversely, where dark images or printing appears on the document to be copied, the light source is not reflected. The photoconductor responds to the reflected light by conducting the positive charge to system ground at each location exposed to the light source. Thus, the surface of the photoconductor contains a latent image of the document to be reproduced wherein the latent image area is represented by, for example, a positive charge.
Alternatively, in, for example, an electrophotographic printer, the photoconductor is exposed to a patterned light source, such as a controllable optical diode (e.g., a semiconductor laser diode). A controller selectively exposes the surface of the photoconductor to the optical diode to produce preselected charge patterns, such as, alphanumeric characters on the surface of the photoconductor. In this manner, the printer is used to produce a page of printed text.
In step three of this process the charge image is developed into a toned, latent image on the surface of the photoconductor. This toned image is created by exposing the surface of the photoconductor to toner particles, which are attracted to the discharged surface areas of the photoconductor. Thus, a toned, latent image is formed on the surface of the photoconductor. In the fourth step of this process, a conventional sheet of paper is fed in a timely manner into the electrophotographic printer in close proximity to the surface of the photoconductor.
The fifth step of this process involves transferring the toned, latent image from the surface of the photoconductor to the sheet of conventional paper. This transfer is typically accomplished by positioning the sheet of paper between the photoconductor surface and a second charge corotron. The second charge corotron operates to attract the toner particles from the surface of the photoconductor toward the corotron. However, since the sheet of conventional paper is disposed between the corotron and the photoconductor, the sheet of conventional paper intercepts the toner particles and the toned, latent image is formed on the surface of the sheet of conventional paper. Thereafter, in the seventh step of this process, the toner particles are affixed to the sheet of conventional paper by fusing the toner particles. This fusing is accomplished by, for example, a heater disposed adjacent the paper and adapted for heating the toner particles to a temperature sufficient for melting and adhering the particles to the sheet of conventional paper.
It should be appreciated that this process is not 100% efficient. Therefore, some cleaning of the photoconductor surface is necessary to remove toner particles that remain thereon and were not transferred to the sheet of conventional paper. Therefore, the seventh step of this process involves cleaning the photoconductor surface by, for example, a mechanical stripper that scrapes against the surface of the photoconductor and removes any remaining residual image. Finally, in the eighth step of this process it is preferable that the photoconductor surface be completely discharged so that any remaining charge placed thereon is removed before the process is repeated again. Removing the charge ensures that the photoconductor surface is completely cleaned of any residual toner. When the photoconductor (sometimes referred to as "OPC") is discharge, the toner particles are no longer attracted to the photoconductor surface.
The electrophotographic process described above has several inherent disadvantages. First, it is generally recognized that the process of transferring the toned, latent image from the photoconductor surface to the sheet of conventional paper is not 100% effective. Thus, the toned image placed on the surface of the sheet of conventional paper is a less than 100% accurate representation of the toned, latent image originally formed on the photoconductor surface. Thus, the ultimate product of the electrophotographic printing process is of a slightly reduced quality because of the inherent shortcomings in the transfer process step.
The above-described electrophotographic process also suffers from an inherent shortcoming that arises from the toned, latent image being formed directly on the photoconductor and the less than perfect transfer process. The disadvantages associated with these two steps necessitate the seventh step in the process of cleaning the photoconductor. Typically, the mechanical stripper is in actual frictional contact with the surface of the photoreceptor so that after a period of time the photoconductor surface is mechanically worn by contact with the cleaning stripper.
The instant invention is directed to overcoming or at least reducing one or more of the problems described above.